Intermediates in a process for the preparation of castanospermine

ABSTRACT

Castanospermine is prepared by starting from 5-(t-BOC)amino-5-deoxy-1,2-O-isopropylidene-α-D-glucuronolactone. Two additional carbons are added to the starting material using ethyl acetate and a strong base and the resulting cyclic hemiketal is subjected to a series of reductions, with intervening removal of protecting groups, to give the castanospermine. A substituted hydroxypyrrolidinone and a substituted hydroxypyrrolidine serve as intermediates in the process.

The present application is a division of application Ser. No.07/492,507, filed Mar. 12, 1990, now U.S. Pat. No. 5,066,807.

BACKGROUND OF THE INVENTION

Castanospermine is a naturally occurring indolizidine alkaloid that hasbeen found to inhibit enzymatic glycoside hydrolysis. Anti-cancer,anti-viral and anti-AIDS activities have also been reported for thecompound. In addition, esters and glycosyl derivatives ofcastanospermine have also been described in the literature (see EuropeanPatent Application 0 297 534) and such compounds have been described asactive as inhibitors of digestive enzymes and useful in treatingdiabetes.

Castanospermine was initially obtained by extraction from its naturalsources and can be obtained in kilogram quantities in that way. However,the process is expensive and would be limited by the availability of theplant sources. More recently, castanospermine has been obtainedsynthetically by a variety of different procedures such as thosedescribed by Bernotas et al., Tetrahedron Letters, 25, 165 (1984); Setoiet al., Tetrahedron Letters, 26, 4617 (1985); Hamana et al., J. Org.Chem., 52, 5492 (1987); and Reymond et al., Tetrahedron Letters, 30, 705(1989). The various procedures are either quite lengthy and low-yieldingand/or non-specific in that they require the separation of significantamounts of intermediate co-products with undesired stereochemistry orthe procedures suffer from other disadvantages.

Thus, for example, although Reymond et al. may emphasize that theirmethology is "highly stereoselective", the yields in a number of stepsare poor. In addition, although Hamana et al. describes his process as"the most efficient to date," it actually makes use of an ozonolysisstep which would limit its value in any large scale syntheses.

SUMMARY OF THE INVENTION

The present invention thus relates to a new process for the synthesis ofcastanospermine which is both short and highly stereoselective. Morespecifically, the present invention relates to a new process for thepreparation of castanospermine starting from5-(t-BOC)amino-5-deoxy-1,2-O-isopropylidene-α-D-glucuronolactone. Theterm t-BOC or BOC, as used above and in the present application, refersto the group t-butoxycarbonyl.

The process of the present invention can be illustrated structurally asfollows: ##STR1##

Specifically, the present invention relates to a process for converting5-(t-BOC)amino-5-deoxy-1,2-O-isopropylidene-α-D-glucuronolactone tocastanospermine which comprises (a) reacting5-(t-BOC)amino-5-deoxy-1,2-O-isopropylidene-α-D-glucuronolactone (I)with ethyl acetate and a strong base in an inert solvent at lowtemperature whereby the ethyl acetate adds across the carbonyl group ofthe lactone to give the corresponding cyclic hemiketal of a β-keto ester(II); (b) hydrogenating the hemiketal catalytically under pressure overa platinum catalyst in ethyl acetate to reduce the β-keto function andgive the β-hydroxy ester (III); (c) treating the β-hydroxy ester withformic acid in an inert solvent with cooling to remove the protectinggroup from the amine followed by basification and internal cyclizationof the resulting amine to give lactam (IV); (d) reducing the lactam withan aluminum hydride reducing agent to give the corresponding pyrrolidine(V); and (e) treating the pyrrolidine first with trifluoroacetic acidwith cooling and then hydrogenating over platinum catalyst underpressure to give castanospermine (VI).

In step (a), the strong base removes an α-hydrogen from the ethylacetate and the resulting anion adds to the carbon atom of the lactonecarbonyl. Lithium diisopropylamine is a preferred strong base for thereaction and tetrahydrofuran is a preferred solvent. The reaction iscarried out with cooling in a dry ice/acetone bath so that thetemperature is about -78° C.

In the hydrogenation in step (b), two epimeric β-hydroxy esters can beformed and the use of platinum oxide in ethyl acetate at a pressure ofabout three atmospheres favors the formation, by a ratio of 7:2 withrespect to the other isomer, of the hydroxy isomer required for thesynthesis of castanospermine. When other solvents are used, poorerratios of the desired isomer are obtained while other catalysts give noreaction. Hydride reducing agents favor the formation of the undesiredhydroxy isomer. Although a mixture of isomers is obtained even under themost favorable conditions, the two isomers obtained can be separated bychromatography and the desired isomer can still be isolated in goodyield (about 79%).

Hydrolysis of Compound III to remove the t-butoxycarbonyl protectinggroup from the amino-group is carried out using formic acid becauseother common hydrolyzing agents work poorly. The hydrolysis actuallygives the formate salt of the resulting amine and a solution of thissalt is basified to convert it to the free amine. Use of a basic ionexchange resin, in the form of a column, is preferred for thisbasification. With the formation of the free amine, internal cyclizationwith the ester function takes place to give the corresponding γ-lactam(IV).

Reduction of the lactam (IV) to the corresponding cyclic amine(pyrrolidine) (V) is accomplished by the use of an aluminum hydridereducing agent in a inert solvent. Lithium aluminum hydride in an ethersolvent such as tetrahydrofuran is preferred for this conversion.

The ketal protecting group is removed from the cyclic amine (V) bytreatment with an acid with cooling. Trifluoroacetic acid at about 0° C.is preferred for this purpose. The resulting product is a cyclichemiacetal which, in the open hydroxy aldehyde form, can recyclize on tothe pyrrolidine nitrogen to give a second ring (a piperidine ring). Theresulting unsaturated bicyclic compound is then hydrogenatedcatalytically under pressure using a catalyst such as platinum oncarbon, with water as the solvent, at a pressure of about threeatmospheres. This procedure gives castanospermine (VI) which isidentical with natural castanospermine.

The 5-(t-BOC)amino-5-deoxy-1,2-O-isopropylidene-α-D-glucuronolactoneused as the starting material in the above process can be obtained from1,2-O-isopropylidene-5-oxo-α-D-glucuronolactone by the following seriesof reactions: ##STR2##

In this process, the 5-oxo compound (hydrated form) is reacted with anO-substituted hydroxylamine, wherein A is the O-substituent, to give thecorresponding 5-oxime which is then hydrogenated catalytically in thepresence of t-BOC-anhydride to give the desired compound. The group A ispreferably benzyl or trimethylsilyl.

The following examples are presented to illustrate the present inventionbut they should not be construed as limiting it in any way.

DETAILED DESCRIPTION OF THE INVENTION Example 11,2-O-Isopropylidene-5-oxo-α-D-glucuronolactone Hydrate

To a cold (-70° C.) solution of dimethyl sulfoxide (10.7 g, 0.14 mol) inmethylene chloride (200 mL) a solution of oxalyl chloride (8.0 mL, 0.09mol) in methylene chloride (50 mL) was added dropwise at such a rate tomaintain the reaction temperature below -55° C. After stirring for 0.5hour below -70° C., a solution of1,2-O-isopropylidene-α-D-glucuronolactone (10.0 g, 0.046 mol) inmethylene chloride (100 mL) was added dropwise while again maintainingthe reaction temperature below -55° C. The addition required 10 min.After stirring at -70° C. for 3 h, triethylamine (18.0 mL, 0.13 mol) wasadded dropwise, again maintaining the temperature below -55° C. Thisaddition required 5-10 min. After an additional 15 min, the cooling bathwas removed, water (2.0 mL) added, and the reaction mixture allowed towarm to ambient temperature. Ethyl acetate (350 mL) was added and theresulting suspension poured through silica gel (250 mL) and eluted withethyl acetate (500 mL). Concentration of the eluate left crude product(10.0 g, 94%). Recrystallization of a sample from ethyl acetatehexane(1:1) gave pure 1,2-O-isopropylidene-5-oxo-α-D-glucuronolactone hydrateas colorless needles: mp 145°-148° C.; 1H NMR (acetone-d₆)δ 1.41 (s,3,CH₃), 1.57(s,3,CH₃), 4.62 (d,1,J=3.1 Hz,H-3), 4.91 (d,1,J=3.7 Hz,H-2),4.98 (d,1,J=3.1 Hz,H-4), 5.26 (s,1,OH), 5.50 (s,1,OH), 6.03 (d,1,J=3.7Hz,H- 1); mass spectrum, m/z (rel intensity) 215 (MH⁺ -H₂ O, 100), 185(15), 157 (12).

Example 2A 1,2-O-Isopropylidene-5-oxo-α-D-glucuronolactone O-Benzyloxime

To a suspension of 1,2-O-isopropylidene-5-oxo-α-D-glucuronolactonehydrate (1.85 g, 7.9 mmol) in benzene (40 mL), O-benzylhydroxylaminehydrochloride (1.28 g, 7.9 mmol) was added and the resulting mixturerefluxed for 3 hours. (Complete dissolution of the hydroxylamine andstarting material occurred during this period.) The solution was thencooled and the solvent removed. Chromatographic purification of theresidual viscous oil over silica gel (100 mL) with ethyl acetate-hexane(1:3) as eluent gave 2.51 g (99%) of1,2-O-isopropylidene-5-oxo-α-D-glucuronolactone O-benzyloxime as acolorless viscous oil which slowly solidified on standing. NMR analysisshowed a single oxime isomer present. An analytical sample was obtainedas colorless prisms by recrystallization from benzene-hexane (1:1): mp83°-85° C.;¹ H NMR (CDCl₃) δ 1.36(s,3,CH₃), 1.52 (s,3, CH₃), 4.86(d,1,J=3.5 Hz,H-2), 4.91 (d,1,J=4.4 Hz,H-3), 5.42 (` AB` subspectra, 2,J_(AB) =13.7 Hz,CH₂), 5.51 (d,1,J=4.4 Hz,H-4), 6.00 (d,1,J=3.5 Hz,H-1),7.37 (m,5,C₆ H₅); ¹³ C NMR(CDCl₃) δ 26.66, 27.34, 60.02, 72.22, 79.60,83.15, 83.23, 107.07, 113.71, 128.54, 128.62, 128.74, 128.83, 135.46,144.52, 162.96; mass spectrum, m/z (rel intensity) 320 (MH⁺, 100), 262(15), 91 (90).

Example 2B 1,2-O-Isopropylidene-5-oxo-α-D-glucuronolactoneO-(trimethylsilyl)oxime

A well-stirred, nitrogen-blanketed mixture of 1,2-O-isopropylidene-5-oxo-α-D-glucuronolactone hydrate (0.45 g, 1.9 mmol) andO-(trimethylsilyl)hydroxylamine (0.24 g, 2.3 mmol) in benzene (30 mL)was heated to reflux, during which time a homogeneous solution wasobtained, and refluxed for 2 h. The reaction was cooled to ambienttemperature and the solvent evaporated at reduced pressure. The residualthick oil was dissolved in ethyl acetate (˜35 mL) and the solutionfiltered through a celite pad to remove any insoluble material. Thefiltrate was concentrated, leaving 0.6 g (˜100%) of crude1,2-O-isopropylidene-5-oxo-α-D-glucuronolactone O-(trimethylsilyl)oximeas an off-white, amorphous solid. This was an ˜3:2 mixture of oximestereoisomers by ¹ H NMR analysis, and was not further characterized.The crude oxime was used without further purification in subsequentreactions: ¹ H NMR (DMSO-d6)δ 6.03 (d,1,J=4.0 Hz) 5.42 (d,1,J=4.3 Hz)5.05 (d,1,J=4.3 Hz), 4.90 (d,1,J=4.0 Hz), 1.44 (s,1), 1.29 (s,l), 0.00(s,9); mass spectrum (CI/CH₄) m/z (rel intensity) 302 (MH⁺,4) 258 (12),230 (100), 172 (40), 95 (60).

Example 3A5-(t-BOC)amino-5-deoxy-1,2-O-isopropylidene-α-D-glucuronolactone fromO-Benzyloxime

To a solution of 1,2-O-isopropylidene-5-oxo-α-D-glucuronolactoneO-benzyloxime (3.16 g, 9.9 mmol) and (BOC)₂ O (2.38 g, 10.9 mmol) inethyl acetate (20 mL) was added 0.5 g of 10% Pd/C and the resultingsuspension stirred for 0.5 h under nitrogen. The catalyst was removed byfiltration and washed with ethyl acetate (10 mL). Fresh Pd/C (0.9 g) wasadded to the filtrate, and the mixture hydrogenated on a Parr apparatusat 3 atmospheres for 60 h. The catalyst was filtered, washed with ethylacetate (15 mL) and the filtrate concentrated. Chromatography of theresidue over silica gel (80 mL) with ethyl acetate-hexane (1:3) aseluent yielded 1.85 g (59%) of5-(t-BOC)amino-5-deoxy-1,2-O-isopropylidene-α-D-glucuronolactone. Ananalytical sample was obtained by recrystallization from ethylacetate-hexane (1:1) as colorless needles: mp 157°-159° C.; ¹ H NMR(CDCl₃) δ 1.35 (s,3, CH₃), 1.46 (s,9, C₄ H₉), 1.52 (s,3,CH₃), 4.78(dd,1,J=8.8,4.2 Hz,H-5), 4.82 (d,1,J=3.7 Hz,H-2), 4.84 (d,1,J=3.0Hz,H-3), 4.95 (dd,1,J=4.2,3.0 Hz,H-4), 5.10 (d,1,J=8.8 Hz,NH), 5.93(d,1,J=3.7 Hz,H-1); mass spectrum, m/z(rel intensity) 316 (MH⁺,5), 288(20), 260 (100), 216 (40).

Example 3B5-(t-BOC)amino-5-deoxy-1,2-O-isopropylidene-α-D-glucuronolactone (I)from O-(trimethylsilyl)oxime

When the procedure of Example 3A was repeated using1.2-O-isopropylidene-5-oxo-α-D-glucuronolactone O-(Trimethylsilyl)oximein place of the O-benzyloxime,5-(t-BOC)amino-5-deoxy-1,2-O-isopropylidene-α-D-glucuronolactone wasobtained in an average yield of about 60%.

Example 4 Ethyl5,7-dideoxy-5-[[(t-butoxy)carbonyl]amino]-1,2-O-(1-methylethylidene)-.alpha.-D-gluco-6-octulo-1,4:6,3-difuranuronate

To a well-stirred, nitrogen-blanketed solution of diisopropylamine (7.7mL, 55.0 mmol) in anhydrous tetrahydrofuran, cooled to -78° C. (dryice/acetone), a 1.6M solution of n-butyllithium in hexane (34.4 mL, 55.0mmol) was added dropwise during 5 minutes. The resulting solution wasstirred for 20 min at -78° C., then ethyl acetate (5.5 mL, 56.2 mmol)was added dropwise during 10-15 min while maintaining the reactiontemperature below -70° C. After 20 min, a solution of5-(t-BOC)amino-5-deoxy-1,2-O-iso-propylidene-α-D-glucuronolactone (I)(5.3 g, 16.8 mmol) in tetrahydrofuran (50 mL) was added dropwise whileagain maintaining the reaction temperature below -70° C. This additionrequired about 20 min. The reaction solution was stirred an additional 2h at -78° C., then allowed to warm to -10° C. and poured onto a stirredmixture of 1N hydrochloric acid (100 mL) and ice (˜100 g). This mixturewas extracted with ethyl acetate (3×100 mL) and the combined extractswere washed with sat. sodium bicarbonate (100 mL) and brine (100 mL),then dried (MgSO₄) and concentrated at reduced pressure. The oilyresidue was flash-chromatographed over silica gel (100 mL) using 3%acetone in methylene chloride as eluent. Pure ethyl5,7-dideoxy-5-[[(t-butoxy)carbonyl]amino]-1,2-O-(1-methylethylidene)-.alpha.-D-gluco-6-octulo-1,4:6,3-difuranuronate(II) (6.6 g, 97%) was obtained as a colorless oil which by ¹ H NMRanalysis was a single isomer, identified by NOE experiments as that inwhich the N-BOC and acetate moieties were trans: [α]_(D) ²⁵ =+10.7° (c2.3, CHCl₃); ¹ H NMR (CDCl₃) δ 6.03 (d,1, J=3.7Hz, H-1), 5.57 (s,1,OH),5.38 (d,1, J=9.5 Hz, NH), 4.88 (dd, 1, J=5.4, 5.4 Hz, H-4), 4.68 (d, 1,J=3.7 Hz, H-2) 4.67 (d, 1, J=5.4Hz, H-3), 4.21 (q, 2,J=7.2 Hz, CH₂ CH₃),3.84 (dd, 1, J=9.5, 5.4 Hz, H-5), 2.82 (d, 1,J=16.3 Hz, H-7), 2.59 (d,1,J=16.3 Hz, H-7'), 1.46 (s,3, CH₃), 1.45 (s,9, t-C₄ H₉), 1.34 (s,3,CH₃), 1.29 (t,3, J=7.2 Hz, CH₂ CH₃); ¹³ C NMR (CDCl₃) δ 13.9, 27.1,27.6, 28.2, 40.8, 59.1, 61.3, 79.8, 80.8, 84.0, 86.7, 101.9, 107.1,113.0, 155.3, 172.3; mass spectrum, m/z (rel intensity) 404 (MH⁺, 80),386 (MH⁺ -H₂ O, 30), 330 (MH⁺ -C₃ H₆ O₂, 100), 286 (40), 214 (25).

Example 5 Preparation of Ethyl5,7-dideoxy-5-[[(t-butoxy)carbonyl]amino]-1,2-O-(1-methylethylidene)-L-glycero-α-D-glucooctofuranuronate(III)

A solution of 10.0 g (24.8 mmol) of ketol-ester II in ethyl acetate (150mL) was hydrogenated at three atmospheres over PtO₂ (4.0 g) catalyst for20 h on a Parr apparatus. The catalyst was filtered off through a bed ofCelite and washed with ethyl acetate (50 mL). The combined filtrate wasconcentrated at reduced pressure, leaving 10.0 g (100%) of an oilymixture of two isomeric amino-diols (a and b) which by hplc analysis[Waters Hypersil ODS (C18, 5μ) column (250 mm×4.6 mm); CH₃ CN(60)/H₂ O(40) eluent; 1.5 mL/min flow rate; about 100 atmospheres pressure;retention time a (the desired isomer)=3.4 min. [b=2.9 min] was a 7:2mixture of the two, with a predominating. This mixture was flashchromatographed over 750 mL of silica gel using 4% acetone in methylenechloride as eluent. Twenty five×125 mL fractions were collected after aforerun of 500 mL. Fractions 10-17 contained pure a (5.0 g), fractions18-23 contained a mixture of a and b (3.5 g) and fractions 24 and 25contained b. Rechromatography of the material from fractions 18-23afforded an additional 2.9 g of ethyl5,7-dideoxy-5-[[(t-butoxy)carbonyl]amino]-1,2-O-(1-methylethylidene)-L-glycero-α-D-gluco-octofuranuronate(a, III) for a yield of 79%. The isolated a slowly crystallized onstanding. An analytical sample was obtained as colorless prisms from(1:4) ether-petroleum ether, bp. 35°-60° C.: mp 102°-104° C.; [α]_(D) ²⁵=+21.8° (c 2.3, CHCl₃);1H NMR (CDCl₃) δ 5.93 (d, 1, J=3.7 Hz, H-1), 5.32(d, 1, J=9.1 Hz, NH), 4.85 (br s, 1, OH), 4.56 (d, 1, J=3.7 Hz, H-2),4.56 (m, 1, H-6), 4.17 (q, 2, J=7.2 Hz CH₂,CH₃), 4.13 (m, 1,H-4), 4.05(d, 1, J=2.2 Hz, H-3), 3.61 (dd, 1, J=9.4, 9.1 Hz, H-5), 3.44 (br s, 1,OH), 2.67 (dd, 1, J=16.2, 9.5 Hz, H-7), 2.44 (dd, 1, J=16.2, 3.6 Hz,H-7'), 1.50 (s, 3, CH3), 1.45 (s, 9, t-C₄ H₉), 1.32 (s, 3, CH₃), 1.27(t,3, J=7.2Hz, CH₂ CH₃); ¹³ C NMR (CDCl₃) δ 14.2, 26.2, 26.8, 28.2,38.6, 51.9, 60.9, 65.4, 74.1, 80.1, 81.1, 84.5, 105.1, 111.6, 157.6,172.6; mass spectrum, m/z(rel intensity) 406 (MH⁺, 32), 350 (MH⁺ -C₄ H₈,35), 334 (MH⁺ -C₄ H₈ O, 25), 306 (MH⁺ -C₅ H₉ O₂, 100), 292 (13), 100(46).

Example 6 [3aR-[3aα,5α(4S*,5R*),6α,6aα]]-4-Hydroxy-5-(tetrahydro-6-hydroxy-2,2-dimethylfuro[2,3-d]-1,3-dioxol-5-yl)-2pyrrolidinone(IV)

To a cold (0°-5° C.) well-stirred, nitrogen-blanketed solution ofBOC-amino-diol III (13.3 g, 32.7 mmol) in methylene chloride (135 mL),98% formic acid (400 mL) was added dropwise during 10 minutes. Thissolution was stirred at 0°-5° C. for 1 h then at ambient temperature for6 h and finally, concentrated to dryness in vacuo at 30° C., leaving12.3 g of thick, viscous oil. This was dissolved in water (50 mL) andadsorbed onto a column of 1L of Dowex 1×2 basic ion exchange resin(prewashed with 1.5L of 1N aqueous sodium hydroxide and then H₂ O toneutrality (˜5.0L)) and eluted with water. After a forerun of 500 mL,five×125 mL fractions, followed by ten×300 mL fractions were collected.Crystalline [3aR-[3aα,5α(4S*,5R*),6α,6aα]]-4-Hydroxy-5-(tetrahydro-6-hydroxy-2,2-dimethylfuro[2,3-d]-1,3-dioxol-5-yl)-2-pyrrolidinone(IV), 6.3 g (73% for the two steps) was obtained from fractions 13-36.An analytical sample was obtained as fine colorless needles byrecrystallization from methanol: mp 263°-265° C.; [α]_(D) ²⁵ =-39.3° (c0.67, H₂ O); ¹ H NMR (DMSO-d₆) δ 7.34 (br s, 1, NH), 5.82 (d, 1, J=3.7Hz, H-1), 5.10 (d, 1, J=4.7 Hz, 3-OH), 5.00 (d, 1, J=4.9 Hz, 6-OH), 4.40(d, 1, J=3.7 Hz, H-2), 4.23 (ddd, 1, J=5.4, 4.2, 1.0 Hz, H-6), 4.18 (dd,1, J=9.6, 2.7 Hz, H-4), 4.11 (dd, 1, J=4.7, 2.7 Hz, H-3), 3.60 (dd, 1,J=9.6, 4.2 Hz, H-5), 2.48 (dd, 1, J=16.6, 5.4 Hz, H-7),1.95 (dd, 1,J=16.6, 1.0 Hz, H-7'), 1.37 (s,3,CH₃), 1.24 (s,3, CH₃); ¹³ C NMR(DMSO-d₆)δ 26.3, 26.8, 41.3, 56.9, 66.5, 73.3, 77.4, 84.9, 104.5, 110.6,175.8; mass spectrum, m/z (rel intensity) 260 (MH⁺, 100), 202 (MH⁺ -C₃H₆ O, 23).

Example 7[3aR-[3aα,5α(2R*,3S*),6α,6aα]]-2-(Tetrahydro-6-hydroxy-2,2-dimethylfuro[2,3-d]-1,3-dioxol-5-yl)-3-pyrrolidinol(V)

To a well-stirred, nitrogen-blanketed suspension of lithium aluminumhydride (2.3 g, 60.0 mmol) in anhydrous tetrahydrofuran (150 mL), lactamIV (3.0 g, 11.5 mmol) was added in portions during 3-5 min at 25° C.Caution: and H₂ evolution. This mixture was refluxed for 20 h thencooled to 0°-5° C. and the reaction quenched by the careful, sequentialaddition of water (2.5 mL), 1N NaOH (2.5 mL) and water 7.5 mL). Thismixture was stirred at about 5° C. for 20 min then filtered through apad of Celite. The collected aluminate salts were washed withtetrahydrofuran (200 mL) and the combined filtrate and wash wasconcentrated to dryness at reduced pressure, leaving 1.7 g of[3aR-[3aα,5α(2R*,3S*),6α,6aα]]-2-(Tetrahydro-6-hydroxy-2,2-dimethylfuro[2,3-d]-1,3-dioxol-5-yl)-3-pyrrolidinol(V) as a white powder. The collected aluminate salts were refluxed with100 mL of tetrahydrofuran-water (9:1) for 45 min. The salts werefiltered, washed with tetrahydrofuran (50 mL) and the combined filtrateevaporated to dryness, leaving 0.5 g more of V for a total yield of 77%.An analytical sample was obtained as fine, colorless needles byrecrystallization from methanol mp 223°-225° C. (dec); [α]_(D) ²⁵ =-5.0(c 0.32, H₂ O); ¹ H NMR (CDCl₃) δ 5.92 (d, 1, J=3.8 Hz, H-1), 4.55 (d,1, J=3.8 Hz, H-2), 4.40 (ddd, J=5.3, 3.6, 1.6 Hz, H-6), 4.25 (d, 1,J=2.6 Hz, H-3), 4.13 (dd, 1, J=7.8, 2.6 Hz, H-4), 3.50 (m, 3, OH, NH),3.18 (ddd, 1, J-11.2, 7.8, 7.6 Hz, H-8'), 3.12 (dd, 1, J=7.8, 3.6 Hz,H-5), 2.86 (ddd, 1, J=11.2, 9.5, 5.1 Hz, H-8), 2.05 (dddd, J=13.8, 9.5,7.6, 5.3 Hz, H-7'), 1.86 (dddd, J=13.8, 7.8, 5.1, 1.6 Hz, H-7), 1.50 (s,3, CH₃), 1.32 (s, 3, CH₃); ¹³ C NMR δ 26.1, 26.6, 35.4, 43.2, 61.6,70.6, 75.6, 77.9, 85.3, 103.8, 110.1; mass spectrum, m/z(rel intensity)246 (MH⁺,100), 188 (MH⁺ -C₃ H₆ O, 52).

Example 8 (+)-Castanospermine

A solution of[3aR-[3aα,5α(2R*,3S*),6α,6aα]]-2-(Tetrahydro-6-hydroxy-2,2-dimethylfuro[2,3-d]-1,3-dioxol-5-yl)-3-pyrrolidinol(V) (0.5 g, 2.0 mmol) in trifluoroacetic-water (9:1) (25 mL) wasstirred, under nitrogen, at ambient temperature for 20 h. The purplesolution was then concentrated in vacuo (40° C.) leaving a thick syrupwhich was dissolved in deionized water (25 mL). This solution wasbasified to a pH of about 9.0 by the addition of 1N aqueous sodiumhydroxide (5.5 mL) and hydrogenated at 3.4 atmospheres over 5% Pt oncarbon (0.3 g) on a Parr apparatus for 16 h. The mixture was filteredthrough a celite pad and the collected catalyst washed with water (2×20mL). The combined filtrate was adsorbed on a column of Dowex 50 W-X8(H⁺) ion exchange resin (10 mL) (prewashed with 200 mL of water) andeluted first with deionized water (200 mL) and then with 1N ammoniumhydroxide solution (twenty×20 mL fractions were collected).(+)-Castanospermine (VI), 0.23 g (61%) was obtained from fractions 1-15.An analytical sample was obtained as colorless prisms byrecrystallization from 90% ethanol: mp 210°-212° C. dec. [lit. 212°-215°C. dec]; [α]_(D) ²⁵ =81.4° (c 1.0, H₂ O) [lit. [α]D²⁵ =+79.7° (C 0.93,H₂ O)]; ¹ H NMR (D₂ O) δ 4.42 (ddd, 1, J=7.0, 4.5, 2.1Hz, H-1), 3.62(ddd, 1, J=10.6, 9.4, 5.1 Hz, H-6), 3.60 (dd, 1, J=9.8, 9.0 Hz, H-8),3.32 (dd, 1, J=9.8, 9.0 Hz, H-7) 3.18 (dd, 1, J=10.8, 5.1 Hz, H-5), 3.08(ddd, 1, J=9.0, 8.8, 8.8 Hz, H-3), 2.34 (dddd, 1, J=13.9, 9.0, 7.0, 2.2Hz, H-2), 2.22 (ddd, 1, J=9.3, 9.0, 8.8 Hz, H-3'), 2.06 (dd, 1, J=10.8,10.6 Hz, H-5'), 2.02 (dd, 1, J=9.8, 4.5Hz, H-8a), 1.71(dddd, 1, J=13.9,9.3, 8.8, 2.1 Hz, H-2'); ¹³ C NMR (D₂ O) δ 35.6, 54.5, 58.3, 71.9, 72.5,73.0, 74.3, 81.9; mass spectrum, m/z(rel intensity) 190 (MH⁺, 50), 172(MH⁺ -H₂ O, 100).

What is claimed is:
 1. A compound selected from ethyl5,7-dideoxy-5-[[(t-butoxy)carbonyl]amino]-1,2-O-(1-methylethylidene)-.alpha.-D-gluco-6-octulo-1,4:6,3-difuranuronate,ethyl5,7-dideoxy-5-[[(t-butoxy)carbonyl]amino]-1,2-O-(1-methylethylidene)-L-glycero-α-D-gluco-octofuranuronate,[3aR-[3aα,5α(4S*,5R*),6α,6aα]]4-hydroxy-5-(tetrahydro-6-hydroxy-2,2-dimethylfuro[2,3-d]-1,3-dioxol-5-yl)-2-pyrrolidinone,and[3aR-[3aα,5α(2R*,3S*),6α,6aα]]-2-(tetrahydro-6-hydroxy-2,2-dimethylfuro[2,3-d]-1,3-dioxol-5-yl)-3-pyrrolidinol.2. A compound according to claim 1 which is[3aR-[3aα,5α(4S*,5R*),6α,6aα]]-4-hydroxy-5-(tetrahydro-6-hydroxy-2,2-dimethylfuro[2,3-d]-1,3-dioxol-5-yl)-2-pyrrolidinone.3. A compound according to claim 1 which is[3aR[3aα,5α(2R*,3S*),6α,6aα]]-2-(tetrahydro-6-hydroxy-2,2-dimethylfuro[2,3-d]-1,3-dioxol-5-yl)-3-pyrrolidinol.